1. Field of the Invention
The present invention relates to an ink suited for ink-jet printers, and also to an ink-jet recording process and apparatus that make a record on paper by causing ink to fly from orifices of a recording head by the action of energy, preferably heat energy. More particularly, it relates to an ink-jet recording process and apparatus that make a record on non-coated paper such as paper for copying, paper for reporting, notepaper, letter paper, bond paper and computer printout paper (continuous business forms) commonly used in offices and homes.
2. Related Background Art
Ink-jet recording systems have the advantages that they make less noise in the course of recording and a recorded image with a high resolution can be obtained at a high speed because of use of a highly integrated head. Inks used in such ink-jet recording systems are those prepared by dissolving various kinds of water-soluble dyes in water or in a mixed solution of water and an organic solvent.
When the water-soluble dyes are used, however, light fastness of recorded images is often questioned because such water-soluble dyes have poor light fastness by nature.
Water fastness of recorded images is also often questioned because the dye is water-soluble. More specifically, if recorded images become wet with rain, sweat, or water from food and drink, they may become blurred or disappear.
Meanwhile, light fastness and water fastness are similarly questioned also in writing utensils such as ball-point pens because water-soluble dyes are mainly used, and various water-based pigment inks for writing utensils have been proposed so that such problems can be settled. Examples of studies on dispersion stability, prevention of ink solidification at pen points and prevention of ball wear of ballpoint pens for the purpose of putting water-based pigment inks into practical use are seen in Japanese Patent Application Laid-Open No. 58-80368, No. 61-200182, No. 61-247774, No. 61-272278, No. 62-568, No. 62-101671, No. 62-101672, No. 1-249869, No. 1-301760, etc. Recently, ball-point pens or markers making use of water-based pigment inks have become commercially available.
Also ink-jet recording inks making use of water-based pigment inks, pigment inks making use of specific water-soluble solvent and polymeric dispersant are proposed in Japanese Patent Application Laid-Open No. 56-147859 and No. 56-147860. Inks making use of a pigment and a dye in combination are also proposed in Japanese Patent Application Laid-Open No. 4-57859 and No. 4-57860.
In ink-jet recording, it is very important for non-volatile components in the ink to rapidly cohere after ejection onto the recording paper. When, however, the conventional water-based pigment inks are used in ink-jet recording, the non-volatile components which have cohered on recording paper are kept present on the recording paper as a solid material after the ink has been fixed thereon. Hence, there has been the problem that print surfaces stain when strongly rubbed or when traced with a highlighter pen (fluorescent-ink pen).
When conventional inks are used to make a record by ink-jet recording on plain paper on which no particular ink-receiving layer is formed, there also has been the problem that leathering may occur, though it differs more or less depending on composition. Accordingly, in order to prevent the feathering, it is proposed to add a highly viscous solvent to ink. The feathering can be prevented by increasing the ink viscosity. However, a highly viscous organic solvent must be added in a large quantity for such purpose, so that the ink comes to have an excessively high viscosity, which brings about the problem that the ejection of ink may become unstable because of a decrease in ejection speed of the ink from nozzles or a decrease in surface tension. There still also has been the problem that the degree of print density or feathering may differ depending on the types of recording paper.
As an attempt to solve such problems, Japanese Patent Publication No. 60-500540 and Japanese Patent Application Laid-open No. 63-159485 disclose techniques in which iodine or the like is added to ink to improve the quality level of prints on a specific recording paper. The techniques disclosed in these publications, however, are not effective for a great variety of recording paper.